1. What is Likelihood Ratio?

The Likelihood Ratio (LR) is a measure of diagnostic test performance that indicates how much a test result will change the odds of having a disease. It combines information about the sensitivity and specificity of the test.

2. How Does the Calculator Work?

The calculator uses the Likelihood Ratio formula:

Where:

• Sensitivity — Probability of a positive test in patients with the disease (true positive rate)
• Specificity — Probability of a negative test in patients without the disease (true negative rate)

Explanation: The LR tells you how much the odds of disease increase with a positive test result.

3. Clinical Interpretation

Interpretation Guidelines:

• LR > 10: Large and often conclusive increase in the likelihood of disease
• LR 5-10: Moderate increase in the likelihood of disease
• LR 2-5: Small increase in the likelihood of disease
• LR 1-2: Minimal increase in the likelihood of disease
• LR < 1: Decreases the likelihood of disease

4. Using the Calculator

Tips: Enter sensitivity and specificity as percentages (0-100%). Both values must be valid (0 ≤ value ≤ 100).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between LR+ and LR-?
A: LR+ is for positive test results (shown here), while LR- is for negative results and uses the formula: (1-Sensitivity)/Specificity.

Q2: How is LR different from predictive values?
A: Unlike predictive values, LR is not affected by disease prevalence, making it more stable across different populations.

Q3: How do I use LR in clinical practice?
A: Multiply the pre-test odds by the LR to get post-test odds: Post-test odds = Pre-test odds × LR.

Q4: What's considered a good LR value?
A: Generally, LR+ > 10 and LR- < 0.1 indicate highly informative tests.

Q5: Can I calculate LR for continuous tests?
A: Yes, but you'll need to define cut-off points and calculate sensitivity/specificity at those points.